1. Field of the Invention
The invention proceeds from a two-quadrant converter according to the preamble of Patent claims 1-3.
2. Discussion of Background
The preamble of the invention refers to a prior art such as is disclosed in EP-A1-0,088,445. There, bridge circuits each having two diodes and two GTO thyristors in the bridge arms provided for the purpose of transmitting energy from and to a reactor, and of transmitting energy via a capacitor to another reactor. The free-wheeling current through one reactor can be controlled alternately by two different bridge arms, so that a reduced switching rate of the semiconductor valves results.
It is known from DE-A-1,964,755 to provide a diode or a switch in parallel with a superconducting coil for the purpose of feeding in, storing and maintaining an electric current in a superconductor circuit.
It is known from Instruments and Experimental Techniques, Vol. 24, No. 5.sup.I, September/October 1971, New York/U.S., E. G. Furman: "Stabilisation of the energy of an accelerator tank circuit", pages 1297 to 1299, to use a two-quadrant converter to excite the magnet of a Betatron, energy being supplied in pulses from a non-stabilised network via a saturable reactor. Feedback into the network of the energy stored in the magnet is prevented by a network-side voltage stabilizing circuit which has a thyristor in series with a reactor. Measures for reducing the switching rate of the semiconductor valves of the two-quadrant converter are not specified.
Additional reference concerning the relevant prior art may be made to IEEE Transactions on Power Systems, Vol. 3, No. 4, November 1988, pages 1418 to 1425. There, two six-pulse converters are connected in series in a Graetz bridge circuit via a superconducting magnet in order to stabilise a network with respect to its active power and reactive power. In this case, the semiconductor valves of the converters need to be overrated in terms of power.